The finding that neurons "encode" various facets of the world was fundamental to our understanding of brain function; the finding that neural coding is plastic is a fundamental principal of nearly equal magnitude. There is a limit to the amount of information that can be gleaned about the mechanisms and meaning of functional plasticity using traditional methods that induce learning and examine the resulting changes in the brain. Using the motor neural prosthetics paradigm, it is possible to control the functional consequence of the firing activity of a group of cells; thus, it is possible to directly change the mapping from the spiking activity of a subset of cells to its effects on the external world. The proposed experiments would address the following questions: 1) To what extent can the motor cortex compensate for changes in the mapping between the activity of a subset of its neurons and the consequences of its activity on the external world? 2) Are different compensation strategies used when different amounts of change are imposed? 3) How selective is the brain in changing the firing correlates of the particular cells whose mapping was changed? A investigation of these issues will reveal insights about the system-level mechanisms of plasticity in a way not possible with traditional methods. [unreadable] [unreadable]